The laser gyroscope may be used to measure the rate of rotation. The principles underlying its operation are described, e.g., in J. Wilson et al.'s "Lasers: Principles and Applications," (Prentice Hall, New York, 1987), at pages 153-157. Two types of laser gyroscopes are known: ring laser gyroscopes, and optical fiber gyroscopes.
The prior art ring laser gyroscopes are comprised of a source of lasing and optical mirrors. At least two laser beams are used in these devices, one travelling clockwise, and the other travelling counterclockwise. The optical path of the light will vary with the rotational motion of the vehicle which is carrying the gyroscope. The light impinging upon the surfaces of the mirrors is generated by one or more laser cells. A major portion of this light is reflected by the mirrors; and a minor portion of the light is transmitted through at least one of the mirrors. The light transmitted through the mirror(s) may be measured by a system containing an optical sensor(s) and a data processor; and the system can thus detect changes in the rotational motion.
One need not use the optical sensing system continually in the ring gyroscope. It is preferred to use this sensor system intermittently for short periods of time when sensing of the motion is required. However, one should keep the light beams within the gyroscope continually travelling from mirror to mirror for proper operation.
A certain portion of the light beams is transmitted through the mirrors, even when the optical sensor is not on. The amount of light lost to transmission through the mirrors is wasted when the optical sensor is not on, for it diminishes the intensity of the optical beams travelling from mirror to mirror.
It is an object of this invention to provide a mirror whose reflectivity can be varied. When such mirror is used in a laser gyroscope, it can be maintained at high reflectivity at all times when the optical sensor is not on and, when the sensor is on, reduced to a lower reflectivity.
It is another object of this invention to provide a laser gyroscope comprised of at least one mirror whose reflectivity can be varied.
It is yet another object of this invention to provide an optical fiber gyroscope comprised of optical fiber which is superconductive and whose optical transmission properties can be varied.